1. Field of the Invention
The present invention relates to an estimation method for a film having the optical anisotropy due to the alignment of molecules, for example, a liquid crystal alignment layer and the like which provides the initial orientation to the liquid crystal molecules in a liquid crystal display device.
2. Description of the Related Art
The crystal rotation method ( described by T. J. Scheffer and J. Nehring in Journal of Applied Physics, Vol. 48, pp.1783, 1977) has been widely employed as an optical method of measuring an angle that liquid crystal molecules in an antiparallel cell make with the reverse of a substrate. In this method, with the linearly polarized light incident on the sample, the optical retardation(phase shift) of the transmitted light which is generated through birefringence is measured as a function of the incident angle. On the other hand, instead of the direct measurement of the dependence of the polarization in the transmitted light on the incident direction, another measuring method in which an analyzer is placed behind a sample and the quantity of light transmitted through the analyzer is monitored as a function of the incident angle is also widely utilized.
However, the above-mentioned conventional techniques have the following problems as pointed out, for example, by K.-Y. Han et al. in Japanese Journal of Applied Physics, Vol. 32, pp. L1242-1244,L277-279 1993.
That is, because the liquid crystal is held between a pair of glass substrates, the refraction at the substrate causes a shift in the incident position of the light on the liquid crystal section, as the incident angle is changed. As the place through which the light passes within the liquid crystal is varied, the polarization of the transmitted light directly reflects the variance in thickness of the liquid crystal layer with the place, which hinders the accurate measurements. The incident angle of the light on the sample is usually changed by rotating the sample so that the relative position between the incident light and the transmitted light also changes, accompanying with the sample rotation. As a result, in order to carry out an accurate polarization measurement of the transmitted light, it is necessary for the positions of an analyzer and the like to be adjusted according to the thickness, the material and the rotation angle of the sample and the measuring efficiency of this method becomes low.
A primary object of the present invention is to provide a method of determining a pretilt angle of liquid crystal molecules with high accuracy, by measuring the incident angle dependence of the polarization of the transmitted light, wherein, instead of controlling the incident angle of the light through the sample rotation, the incident light is first condensed by a lens and the light incident on a sample is made to contain components with a plurality of incident angles, simultaneously.
Accordingly, in light of above problems, an object specified by the present invention is to provide a method of measuring a liquid crystal pretilt angle which determines a liquid crystal pretilt angle by setting the incident light with a given polarization on a liquid crystal sample and measuring the polarization of the transmitted light; wherein:
being condensed by a lens, said incident light with a given polarization is turned to have the incident angle of being distributed continuously and set incident on said liquid crystal sample; and
the dependence of the polarization of said transmitted light on the incident angle is measured and thereby a pretilt angle of said liquid crystal sample is determined.
Another object of the present invention is to provide a method of measuring a liquid crystal pretilt angle which determines a liquid crystal pretilt angle by setting the incident light with a given polarization on a liquid crystal sample and measuring the polarization of the transmitted light;
wherein:
said liquid crystal sample comprises a liquid crystal material, transparent substrates sandwiching that liquid crystal material and hemispherical prisms which are placed on both of outer sides of the transparent substrates and have approximately the same refractive index as that of those transparent substrates; and
by means of hemispherical prisms, said incident light with a given polarization is turned to have the incident angle of being distributed continuously and set incident on said liquid crystal sample; and
the dependence of the polarization of said transmitted light on the incident angle is measured and thereby a pretilt angle of said liquid crystal sample is determined.
In the method of measuring a liquid crystal pretilt angle in accordance with the present invention, as mentioned above, the use of a lens or hemispherical prisms enables turning of the polarized light to have the incident angle of being distributed continuously and set incident on a liquid crystal sample without rotating the sample. Therefore, the deterioration in accuracy, resulting from non-uniformity of the sample, does not occur and a pretilt angle of the liquid crystal can be measured with accuracy as well as high speed.
Another object of the present invention is to provide an equipment of measuring a liquid crystal pretilt angle; comprising:
a light source;
a polarizer which polarizes the emitted light from that light source;
a holder which holds a liquid crystal sample as an object of the measurement;
lenses placed before and behind that holder;
a means for measuring, with the light having passed through said liquid crystal sample, the amplitude ratio of said transmitted light and/or the optical retardation of said transmitted light; and
a means for determining a liquid crystal pretilt angle from said measured polarization.
An equipment of measuring a liquid crystal pretilt angle according to the present invention, has such an arrangement as described above that can carry out the above-mentioned method of measuring a liquid crystal pretilt angle favourably.
In the present invention, a lens or hemispherical prisms are utilized in incidence of the polarized light on the liquid crystal sample so that it is possible to set the incident light in a state where the incident angle is distributed continuously, without rotating the sample. Therefore, a deterioration in accuracy, resulting from non-uniformity of the sample, does not occur and a pretilt angle of the liquid crystal can be measured with accuracy as well as high speed.